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"Molybdenum is an essential trace element for plant growth. Since it occurs in natural waters only in trace amount, a very sensitive method of determination is needed. Using the following polarographic method, it is possible to determine 5·10-10 mol/L resp. 50 ng/L.The principle of the method is based on the reaction between the molybdate ion MoO42- and the complexing agent 8-hydroxy-7-iodo-quinoline-5-sulfonic acid (H2L) to form a MoO2L22- complex, which is adsorbed on the mercury electrode. The adsorbed Mo(VI) is reduced electrochemically to the Mo(V) complex. The hydrogen ions present in the solution oxidize Mo(V) again spontaneously to form the Mo(VI) complex, which is thus newly available for electrochemical reduction. This catalytic reaction is the reason for the high sensitivity of the method.Tungsten W(VI) exhibits practically the same electrochemical behavior as molybdenum, but is not described in detail in this Application Bulletin."

The metals Cd, Co, Cu, Fe, Ni, Pb, and Zn are determined in the sub-ppb range (limit of detection 0.05 µg/L) by means of stripping voltammetry. The DP-ASV method is used for Cd, Cu, Pb, and Zn whereas Co, Ni, and Fe are determined by means of the DP-CSV method (dimethylglyoxime or catechol complexes).Use of the VA Processor and the sample changer allows automatic determination of the above metal ions in one solution. The method has been specially developed for trace analysis in the manufacture of semiconductor chips based on silicon. It can naturally also be employed successfully in environmental analysis.

In most electrolytes the peak potentials of lead and tin are so close together, that a voltammetric determination is impossible. Difficulties occur especially if one of the metals is present in excess.Method 1 describes the determination of Pb and Sn. Anodic stripping voltammetry (ASV) is used under addition of cetyltrimethylammonium bromide. This method is used when:• one is mainly interested in Pb• Pb is in excess• Sn/Pb ratio is not higher than 200:1According to method 1, Sn and Pb can be determined simultaneously if the difference in the concentrations is not too high and Cd is absent.Method 2 is applied when traces of Sn and Pb are found or interfering TI and/or Cd ions are present. This method also uses DPASV in an oxalate buffer with methylene blue addition.

The bromine number and bromine index are important quality control parameters for the determination of aliphatic C=Cdouble bonds in petroleum products. Both indices provide information on the content of substances that react withbromine. The difference between the two indices is that the bromine number indicates the consumption of bromine in gfor 100 g sample and the bromine index in mg for 100 g sample.This Application Bulletin describes the determination of the bromine number according to ASTM D1159, ISO 3839, BS2000-130, IP 130, GB/T 11135 and DIN-51774-1. The bromine index determination for aliphatic hydrocarbons is described according to ASTM D2710, IP 299, GB/T 11136 and DIN 51774-2. For aromatic hydrocarbons the determination of the bromine index is described according to ASTM D5776 and SH/T 1767. UOP 304 is not recommended for the determination of the bromine number or bromine index because its titration solvent contains mercuric chloride.

The determination of the physical and chemical parameters as electrical conductivity, pH value, p and m value (alkalinity), chloride content, the calcium and magnesium hardness, the total hardness, as well as fluoride content are necessary for evaluating the water quality. This bulletin describes how to determine the above mentioned parameters in a single analytical run.Further important parameters in water analysis are the permanganate index (PMI) and the chemical oxygen deman (COD). Therefore, this Bulletin additionally describes the fully automated determination of the PMI according to EN ISO 8467 as well as the determination of the COD according to DIN 38409-44.

Maleic and fumaric acid can be reduced electrochemically to succinic acid. In acidic solutions a differentiation of the two acids is not possible since both are reduced at the same potential. On the other hand, separation at pH 7.8...8.0 is easily possible since fumaric acid is now more difficult to reduce at the lower proton concentration (as a result of cis-trans isomerism) than maleic acid.

The formol number represents a further parameter for the characterization of fruit and vegetable juices. As this is merely an index (the formalin number does not deal with the molecular size, nor with the quantity of amino acids), the conditions of the titration can be adapted to meet practical needs. This concerns mainly the pH value of the endpoint of the SET titration (pH = 8.5, pH = 9.0, pH = 9.2, etc.).

Mixtures of aluminum and magnesium ions can be analyzed automatically using potentiometric titration. The excess DCTA is back-titrated with copper(II) sulfate solution after the addition of 1,2-diaminocyclohexanetetraacetic acid (DCTA) and complex formation. The ion-selective copper electrode is used here as the indicator electrode. First, the aluminum is determined in acidic solution and then the magnesium in alkali solution.

This Bulletin describes the voltammetric determination of aluminum in water samples down to a concentration of 1 μg/L. An aluminum complex is formed with alizarin red S (DASA) and enriched at the HMDE. The following determination employs differential pulse adsorptive stripping voltammetry (DP-AdSV). Disturbing Zn ions are eliminated by addition of CaEDTA.

This Bulletin, using practical examples, indicates how the user can achieve optimum pH measurements. As this Bulletin is intended for actual practice, the fundamentals - which can be found in numerous books and publications - are treated only briefly.